CVE-2021-21299Multiple Transfer-Encoding headers misinterprets request payload

Official description

hyper is an open-source HTTP library for Rust (crates.io). In hyper from version 0.12.0 and before versions 0.13.10 and 0.14.3 there is a vulnerability that can enable a request smuggling attack. The HTTP server code had a flaw that incorrectly understands some requests with multiple transfer-encoding headers to have a chunked payload, when it should have been rejected as illegal. This combined with an upstream HTTP proxy that understands the request payload boundary differently can result in "request smuggling" or "desync attacks". To determine if vulnerable, all these things must be true: 1) Using hyper as an HTTP server (the client is not affected), 2) Using HTTP/1.1 (HTTP/2 does not use transfer-encoding), 3) Using a vulnerable HTTP proxy upstream to hyper. If an upstream proxy correctly rejects the illegal transfer-encoding headers, the desync attack cannot succeed. If there is no proxy upstream of hyper, hyper cannot start the desync attack, as the client will repair the headers before forwarding. This is fixed in versions 0.14.3 and 0.13.10. As a workaround one can take the following options: 1) Reject requests that contain a `transfer-encoding` header, 2) Ensure any upstream proxy handles `transfer-encoding` correctly.

Affected packages & fixed versions

Affected products (as reported)

References

• https://portswigger.net/research/http-desync-attacks-request-smuggling-reborn x_refsource_MISC
• https://rustsec.org/advisories/RUSTSEC-2021-0020.html x_refsource_MISC
• https://github.com/hyperium/hyper/security/advisories/GHSA-6hfq-h8hq-87mf x_refsource_CONFIRM
• https://crates.io/crates/hyper x_refsource_MISC
• https://github.com/hyperium/hyper/commit/8f93123efef5c1361086688fe4f34c83c89cec02 x_refsource_MISC